Glaucoma is a disease condition of the eye in which increased intraocular pressure (IOP) is created by blockage of the drainage mechanism for the aqueous fluid produced in the anterior portion of the eye. Such aqueous outflow conditions are usually treated by topical drugs in the form of eye drops, but may result in surgical treatment if drug treatment becomes ineffective due to loss of response to the drug or poor patient compliance.
Ophthalmic research has indicated that the greatest resistance to aqueous outflow is in the trabecular meshwork, more specifically, the juxtacanalicular tissue at the inner wall of Schlemm's canal (Grant, M. W., Arch. Ophthalmol. 1963; 69:783-801.) Traditional glaucoma surgery such as trabeculectomy, involves a flap dissection of the eye and the removal of a portion of scleral tissue and of the trabecular meshwork to bypass the normal aqueous outflow pathway and form a direct flow path from the anterior chamber. The aqueous fluid is directed posteriorly under the surgical flap and to a sub-conjunctival lake known as a bleb. Post-surgical complications and bleb management are significant issues with trabeculectomy and similar procedures.
Recently developed surgical treatments for glaucoma involve surgically accessing Schlemm's canal by manner of one or more surgical flaps and subsequently dilating the canal to increase aqueous humor drainage into the natural drainage pathway instead of a bleb. The mechanisms involved in dilating Schlemm's canal to aid aqueous outflow are not fully elucidated. Dilation or expansion of the canal may cause a direct communication between Schlemm's canal and the juxtacanalicular space and may enhance aqueous outflow (Smit, B. A., Johnstone, M. A., Ophthalmology, 2002; 109:786-792). In addition, dilation of the canal may also limit the ability of the inner wall to be distended outward by increased intraocular pressure and press against the outer wall to increase aqueous outflow resistance (Ellingsen, B. A., Grant, W. M., Investigative Ophthalmology, 1972; 11(1): 21-8).
Various approaches and devices for glaucoma surgery involving Schlemm's canal have been described in the prior art. Stegmann, et al. in U.S. Pat. No. 5,486,165 disclose a microcannula designed for delivery of substances to Schlemm's canal during glaucoma surgery. In US 2002/0013546, Grieshaber, et al. disclose a device for holding an expanded lumen of Schlemrnm's canal in a permanently expanded position. Lynch, et al. in U.S. Pat. No. 6,464,724 describe a stent device to expand and maintain the patency of Schlemm's canal. Neuhann in U.S. Pat. No. 6,494,857 describes an implantable longitudinally curved tubular device.
Other methods for improving aqueous humor drainage into Schlemm's canal involve placing a shunt that forms a fluid passage between the anterior chamber and the canal. See Lynch et al. in U.S. Pat. No. 6,450,984, Hill in U.S. Pat. No. 6,533,768 and Gharib et al. in US 20020165478.
Cholinergic drugs such as pilocarpine are the oldest effective medical treatment for glaucoma. These drugs work by a mechanical action by increasing ciliary muscle tone that pulls the scleral spur adjacent to the trabecular meshwork toward a posterior and inward direction. Tension is thereby applied to the trabecular meshwork, opening the intertrabecular spaces, increasing aqueous outflow, and reducing intraocular pressure. The present invention describes an implant that resides within Schlemm's canal of the eye and provides tension to the trabecular meshwork similar to the action of cholinergic or miotic drugs. The use of an implant provides continuous tension and increase in aqueous outflow without re-administration of a drug and without drug side effects. In addition, since the implant applies tension to the trabecular meshwork directly, optical effects to the eye such as fluctuating myopic shift and decreased vision in dim illumination produced by cholinergic drugs are avoided.
While the prior art describes various ways to bypass or to stent the lumen of Schlemm's canal, it does not teach a way to increase aqueous outflow by applying non-drug induced tension to the trabecular meshwork at the inner wall of the canal. The present invention describes a novel approach in surgical treatment of glaucoma by placing an implant in Schlemm's canal that is designed to impart mechanical tension to the interfacing trabecular meshwork on the inner wall of the canal, thereby increasing aqueous outflow and reducing intraocular pressure.
This invention is directed at an ophthalmic implant, which may be directly inserted into Schlemm's canal to improve aqueous outflow through the normal trabeculocanalicular pathway for an extended period of time. The invention is directed to embodiments of and materials for such an implant, and also to tools for placing the implant by minimally invasive methods.